Petrogenesis of the island-arc complexes of the Chara zone,East Kazakhstan |
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| Authors: | V A Simonov I Yu Safonova S V Kovyazin |
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| Institution: | 1.Institute of Geology and Mineralogy, Siberian Branch,Russian Academy of Sciences,Novosibirsk,Russia |
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| Abstract: | The study of clinopyroxenes and melt inclusions provided direct (independent on secondary alteration) information on the petrogenesis
of the island arc complexes of the Chara zone, East Kazakhstan. It was shown that magmatism of this zone evolved from primitive
island-arc systems with boninites to mature island arc with calc-alkaline melts. In terms of trace and rare-earth element
distribution, the melt inclusions in the clinopyroxenes of the Chara zone differ from mid-ocean ridge basalts, being closer
to the island-arc calcalkaline series. Based on inclusion composition, the parental melts of the considered complexes crystallized
within 1150–1190°C with decreasing iron, magnesium, calcium, and sodium contents. Simulation based on melt inclusion data
in clinopyroxenes indicates that the melts contained up to 1 wt % water, which was confirmed by direct ion-microprobe determination
of 0.84 wt % H2O in the inclusions. Calculated liquidus temperatures are consistent with homogenization temperatures of the inclusions. Our
calculations on the basis of inclusion data testify that the primary melts of the studied basaltic series of the Chara zone
were generated from the mantle protolith within temperatures of 1350–1530°C at depths of 50–95 km. Similar parameters are
typical of the generation of the tholeiitic and boninitic island-arc magmas in the modern ocean-continent transition zones
of the Pacific type. In general, the study of clinopyroxenes and melt inclusions suggests that the considered complexes of
the Chara zone were formed with the participation of tholeiitic and calcalkaline volcanogenic systems of basaltic, basaltic
andesite, and, possibly, boninitic composition in the paleogeodynamic setting of evolving ancient island arc. |
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